Six days after Edward J. Markey was elected to the US Senate, five Democratic candidates are already running to replace him in the US House of Representatives.

Middlesex County Sheriff Peter J. Koutoujian of Waltham jumped in the race for the Fifth Congressional District with a video announcement on Monday morning. State Senator Karen Spilka of Ashland, who previously said she is running, kicked off her campaign with an event in Framingham on Monday evening.

There are three other declared Democratic contenders in the heavily Democratic and largely suburban district that runs from Revere to Lexington to Framingham to Holliston: state Representative Carl M. Sciortino of Medford, and state Senators Will Brownsberger of Belmont and Katherine Clark of Melrose.

Koutoujian, a former state representative who became sheriff in 2011, spoke about his family’s immigrant roots and called public service his “life’s work” in his announcement.

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“We need to know that the next representative hears the voices and sees the faces of those that they represent and, most importantly, can get things done to make their lives better,” he said
in the video. “I have dedicated my life to doing exactly that and I’m ready to bring those progressive values and a lot of hard work to Washington.”

Spilka noted her record of working to pass laws related to the economy, health care, the environment, and programs for children, according to a copy of her prepared remarks shared by her campaign.

“[T]his race will be about who can best deliver on our progressive principles in a Congress mired in gridlock and obstructionism,” Spilka was scheduled to say, according to the prepared remarks.

Warren Tolman, a former state senator, whose name had been floated as a potential candidate in recent days, said on Monday he would not run for the seat.

The date of the special election has not been set because Markey has not officially stepped down to be sworn in as a US senator. After that resignation takes effect, state election law calls for Governor Deval Patrick to schedule a special election for a date 145 to 160 days later, which probably means that the special election will be held in December with an earlier primary contest.

Also on Wednesday, the campaigns publicly discussed reviving the “People’s Pledge,” a pact designed to limit outside spending in the race. Sciortino and Brownsberger have called for such a pledge in the special election. Campaign aides to the three other candidates said they were open to some version of the agreement pioneered by Democrat Elizabeth Warren and Republican Scott Brown in the 2012 US Senate contest.

Warren and Brown signed a pledge that effectively limited outside spending in their hotly contested race. The pact stipulated that every time an outside group spent money on advertisements to benefit a candidate, that candidate was required to make a donation to charity.

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